Technical Field
The present invention relates to a controller for a battery system including a generator, electrical loads, a lead storage battery, and a high performance storage battery.
Related Art
As described in JP-A-2012-80706, a battery system is proposed which includes a storage battery which is inexpensive but has lower durability under charge and discharge, and a high performance storage battery, which is expensive but has higher-power and higher-energy density and has higher durability under charge and discharge. The battery system is installed in a vehicle using an engine as a driving source.
In the battery system, a generator, electrical loads and a lead storage battery, and a high performance storage battery are electrically connected via a low-cost opening and closing switch. Operation of the opening and closing switch switches the generator, the electrical loads and the lead storage battery and the high performance storage battery to an electrically conducting state or an interrupted state, which appropriately use the two batteries.
However, if the generator, the electrical loads and the lead storage battery and the high performance storage battery are electrically connected by using the opening and closing switch, a large current easily flows from the generator or the lead storage battery to the high performance storage battery. In a state where a large current is flowing to the high performance storage battery, if the generator, the electrical loads and the lead storage battery and the high performance storage battery are interrupted, the large current is received by the lead storage battery, thereby rapidly increasing the terminal voltage of the lead storage battery. Specifically, if internal resistance of the lead storage battery is larger, the amount of increase of the terminal voltage of the lead storage battery increases. Hence, the terminal voltage of the lead storage battery can exceed withstand voltages of the electrical loads.